The broad, long-term objectives of this proposal are to characterize the structure, regulation and function of members of the protein tyrosine phosphatase (PTP) family of enzymes, focussing primarily on the receptor-like PTPs. The actions of PTPs and protein tyrosine kinases (PTKs) are integrated in vivo to control such fundamental processes as growth and proliferation, differentiation, migration, metabolism and cytoskeletal function. Disruption of the delicate balance between the action of PTPs and PTKs has been implicated in the etiology of human diseases, including cancer, diabetes and inflammation. Therefore, the characterization of the PTPs is a prerequisite to gaining a complete understanding of the physiological consequences of tyrosine phosphorylation under normal and disease conditions. This competitive renewal continues an investigation of the regulation and function of two RPTPs, PTPmu and DEP-1. Both of these PTPs show enhanced expression in confluent, compared to sparse cell cultures. Functional links between these enzymes and the suppression of tyrosine phosphorylation-dependent signalling pathways in confluent cells will be established and characterized. These studies will utilize endothelial cell model systems and insights into the control of angiogenesis are anticipated. In addition, experiments are proposed to test the hypothesis that redox-dependent inhibition of PTP function is one mechanism that underlies the transactivation of PTK-dependent signalling pathways following stimulation of G protein coupled receptors (GPCRs). GPCR- regulated PTPs will be identified and characterized. In general these studies will entail definition of the physiological substrate specificity and mechanism for regulation of these PTPs. Extensive use will be made of substrate-trapping mutant forms of the PTPs, a technology developed in the lab, and mass spectrometry-based protein sequencing. The characterization of these enzymes should provide a novel perspective on the control of cell growth and proliferation. The Specific Aims of the proposal are (1) to characterize the function of PTPmu as a regulator of survival signals in endothelial cells, (2) to characterize the regulation and function of DEP-1 in the control of cell growth and proliferation and (3) to explore the potential of reversible oxidation of PTPs as a mechanism for regulation of mitogenic signalling.